One of Mitt Romney’s top strategists today accused President Obama and his political staff of waging a reelection campaign that has descended from petty distortions to “unbelievable exaggerations that diminish the office of the president and insult the American people.”

Adviser Eric Fehrnstrom added: “I don’t think a world champion limbo dancer could get any lower than the Obama campaign right now.”

An Obama spokeswoman accused the Romney campaign of “faux outrage” over a TV commercial not created by the Obama campaign.

Fehrnstrom’s criticism came during a three-minute opening statement he delivered at a media briefing before Romney launches a bus tour on Saturday.

It also came at the conclusion of a week when an Obama-supporting super PAC announced an ad - largely discredited by fact-checking organizations - suggesting Romney is to blame for a woman’s death because her husband lost his health insurance years earlier after being laid off from a company owned by Romney’s former employer, Bain Capital.

The Romney campaign has been incensed at the suggestion the candidate caused a person’s death.

“When you start running ads accusing your opponent of killing people, then you have lost credibility,” Fehrnstrom later told reporters during the briefing.

He added: “We are betting that a substantive campaign, conducted on the high ground and focused primarily on jobs and the economy, will trump a campaign that is designed to appeal to our worst instincts.”

She said in a statement: “Mitt Romney won the Republican primary only by tearing down each of his opponents with ruthlessly negative campaigning, including ads funded by outside allies. His campaign has questioned whether the president understands what it is to be American, attacked his patriotism, and is currently running an ad that a former president and authors of the welfare-to-work legislation have called a flat-out lie. When the Romney campaign finally reaches the high ground, we look forward to greeting them there.”

Hours after the briefing, the Romney campaign unveiled the new commercial echoing Fehrnstrom’s criticisms.

“What does it say about a president’s character when his campaign tries to use the tragedy of a woman’s death for political gain?” the commercial says. “Doesn’t America deserve better than a president who will say or do anything to stay in power?”

Another senior Romney adviser, who addressed reporters on the condition he not be identified by name, dismissed three recent polls by Fox News, Reuters/Ipsos and CNN showing Obama opening up to a 9 percentage point lead over Romney.

The senior adviser said there had been no “precipitating event” to justify such a large shift from what has been a close race when underlying elements in polls still show favorable signs for Romney.

“Guys, it’s the middle of summer. It’s the doldrums. It’s the middle of the Olympics. There has been no national news, anything that would push these numbers from minus three to minus nine points,” the adviser said. “That’s a big jump. You have to have some kind of precipitating event to move numbers.”

The adviser suggested future surveys could similarly swing back in Romney’s favor.

Romney’s bus tour marks an intense period of swing-state campaigning and could also feature the announcement of his vice presidential running mate.

The tour begins Saturday morning with an appearance at the USS Wisconsin in Norfolk, Va., an Iowa-class battleship that carries the symbolism of being named for an important 2012 political battleground and also is the home of one of Romney’s prospective running mates, US Representative Paul Ryan.

Romney’s Virginia visit then takes him to a larger rally in Norfolk, a stop at a small business in Ashland, Va., before another rally in Manassas, Va.

Democrats plan to shadow Romney with their own bus tour whose speakers will include state Representatives Kathi-Anne Reinstein of Revere and David Linsky of Natick. They have been among a group of Massachusetts legislators who have been traveling the country speaking about Romney’s record as governor from 2003 to 2007.

On Sunday, Romney’s tour resumes in North Carolina, a battleground where the Democrats will hold their national convention starting Sept. 4. His stops include a visit to the NASCAR Technical Institute in Mooresville, N.C., and “Smokey’s Shack,” a barbecue joint in Morrisville, N.C.

On Monday, Romney will tour Florida and on Tuesday he will travel through Ohio.

He is slated to be joined in Virginia by Governor Bob McDonnell, in Florida by Senator Marco Rubio, and in Ohio by Senator Rob Portman, three more prospective running mates.

Those scheduled joint appearances have prompted questions about whether Romney would upstage McDonnell, Rubio, or Portman by taking his final choice for vice president with him on the bus tour, or wait until after the tour ends Tuesday to announce his running mate.

The Romney campaign has been stoking speculation with tweets promising an announcement “soon,” but it has not released anything more specific.

“I don’t have any guidance for you on that other than you should download by VP app,” Fehrnstorm said at the briefing, referring to a smartphone application recently created by the campaign.

The bus tour follows a European and Middle East tour Romney took in late July and early August, but marks his most concentrated spate of campaigning domestically since a previous bus tour in June.

Romney had no public events scheduled today but worked from his campaign headquarters in the North End.